The present invention is directed to improved polybutadiene compositions for use in molded golf ball cores. The improved polybutadiene compositions utilize a blend of two particular butadiene rubbers synthesized through the use of neodymium and cobalt-containing catalysts. Each of the polybutadiene blends contains an ultra-high Mooney viscosity polybutadiene. The use of such a blend of butadiene rubbers increases the resiliency of the ball. In addition, significantly improved mixing properties are achieved. The present invention is also directed to golf balls and cores produced by utilizing the improved polybutadiene compositions.
Two of the principal properties involved in the performance of golf balls are resilience and hardness. Resilience is determined by the coefficient of restitution (referred to as xe2x80x9cC.O.R.xe2x80x9d), also expressed as the constant xe2x80x9cexe2x80x9d, which is the ratio of the relative velocity of two elastic spheres after direct impact to that before impact, or more generally, the ratio of the outgoing velocity to incoming velocity of a rebounding ball. As a result, the coefficient of restitution (i.e. xe2x80x9cexe2x80x9d) can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision. Hardness is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the ball""s diameter. The lower the compression value, the harder the material.
Resilience (C.O.R.), along with additional factors such as clubhead speed, angle of trajectory, and ball configuration (i.e. dimple pattern), generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors of concern among manufacturers are the coefficient of restitution (C.O.R.) and the surface configuration of the ball.
In this regard, the coefficient of restitution of a golf ball is generally measured by propelling a ball at a given speed against a hard surface and electronically measuring the ball""s incoming and outgoing velocity. The coefficient of restitution must be carefully controlled in all commercial golf balls in order for the ball to be within the specifications regulated by the United States Golfers Association (xe2x80x9cU.S.G.A.xe2x80x9d). Along this line, the U.S.G.A. standards indicate that a xe2x80x9cregulationxe2x80x9d ball cannot have an initial velocity (i.e. the speed off the club) exceeding 255 feet per second (250 feet per second with a 2% tolerance). Since the coefficient of restitution of a ball is related to the ball""s initial velocity (i.e. as the C.O.R. of a ball is increased, the ball""s initial velocity will also increase), it is highly desirable to produce a ball having a sufficiently high coefficient of restitution to closely approach the U.S.G.A. limit on initial velocity, while having an ample degree of hardness (i.e. impact resistance) to produce enhanced durability.
The coefficient of restitution (C.O.R.) in solid core balls is a function of the composition of the molded core and of the cover. In balls containing a wound core (i.e. balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings.
Polybutadiene has been utilized in forming golf ball cores. Prior artisans have investigated utilizing various grades of polybutadiene in core compositions. For example, such attempts are described in U.S. Pat. Nos. 5,385,440; 4,931,376; 4,683,257; 4,955,613; and 4,984,803; and in Japanese Patent References JP 58225138 and JP 7268132, all of which are hereby incorporated by reference. Although some of the core compositions described in these disclosures are satisfactory, a need remains for an improved composition for forming golf ball cores.
Accordingly, it is an object of the present invention to provide an improved core composition which, when utilized to formulate golf ball cores, produces golf balls exhibiting enhanced C.O.R. and improved processing.
These and other objects and features of the invention will be apparent from the following summary and description of the invention and from the claims.
The present invention achieves all of the foregoing objectives and provides, in a first aspect, a golf ball comprising a core formed from a composition including two particular types of polybutadiene, and a cover disposed about the core. The first polybutadiene utilized in the core is polymerized in the presence of a cobalt or a cobalt-based catalyst and, prior to curing, has a Mooney viscosity from about 65 to about 85. The second polybutadiene is polymerized in the presence of a neodymium or neodymium-based catalyst. In some applications, a nickel-based catalyst may be utilized instead of or in addition to the cobalt catalyst in forming the first polybutadiene. And, the second polybutadiene may be polymerized in the presence of a lanthanide series catalyst instead of or in addition to the neodymium catalyst. The golf ball also includes one or more cover layers generally surrounding the core.
In yet another aspect, the present invention provides a golf ball comprising a core formed from a composition including from about 80 parts to about 120 parts by weight of certain elastomer components, and at least about 60 parts by weight of non-elastomer components. The golf ball further includes a polymeric cover disposed about the core. The elastomer components include a first polybutadiene, synthesized in the presence of a cobalt or nickel catalyst, which prior to curing, exhibits a Mooney viscosity of from about 65 to about 85. The elastomer components also include a second polybutadiene that is synthesized in the presence of a neodymium or lanthanide series catalyst.
In yet another aspect, the present invention provides a golf ball comprising a core formed from a composition that includes two particular types of polybutadiene, and a polymeric cover that is disposed about the core. The core composition includes a first polybutadiene which prior to curing, has a polydispersity of from about 1.9 to about 3.9 and has a Mooney viscosity of from about 65 to about 85. The first polybutadiene is synthesized in the presence of a cobalt or nickel catalyst. The core composition further includes a second polybutadiene synthesized in the presence of neodymium or a lanthanide catalyst.
The present invention also provides, in yet another aspect, a composition that is adapted for forming a golf ball core. The composition comprises a first polybutadiene having a Mooney viscosity of from about 65 to about 85, in which the first polybutadiene is synthesized in the presence of a cobalt or nickel-based catalyst. The composition further comprises a second polybutadiene having a Mooney viscosity of from about 30 to about 65 and which is synthesized in the presence of a neodymium or lanthanide series catalyst. The composition further comprises at least one crosslinking agent.
Furthermore, the present invention provides a method for producing a golf ball which comprises combining two particular types of polybutadiene to form a core composition, molding the core composition to form a golf ball core, and subsequently forming a cover about the golf ball core to produce the golf ball. The golf ball core is formed from a first polybutadiene having a Mooney viscosity of from about 65 to about 85 and a polydispersity of from about 1.9 to about 3.9. The second polybutadiene is synthesized in the presence of a neodymium or lanthanide series catalyst.
Further scope of the applicability of the invention will become apparent from the detailed description provided below.